Preheat broiler. Broil bread until golden, about 1 minute per side. Melt butter in heavy large saucepan over low heat. Add onions and cook 30 minutes, stirring occasionally. Add broth and next 4 ingredients. Increase heat and bring to boil. Reduce heat. Add Port. Cover and simmer 5 minutes. (Can be prepared 1 day ahead. Cover soup and refrigerate. Bring to simmer before continuing.) Preheat broiler. Place bread in 4 ovenproof bowls; place bowls in baking dish. Ladle soup into bowls. Sprinkle with Swiss cheese. Top with Parmesan. Broil until cheese melts and turns golden, about 1 minute. Serve hot. Bon Appetit/August/89 Scanned & fixed by Di and Gary